5i8 



MOSSES AND FERNS 



CHAP. 



Spore for the nucleus — if his statement is correct, S. cuspidata 

 differs very remarkably from other investigated species in the 

 development of the gametophyte. 



Miss Lyon (2) found in both vS'. apus and US', rupestris a 

 much greater development of the primary prothallial tissue than 

 is found in 5'. Kraussiana. To judge from her figures 54 and 

 55, there are two types of prothallium in S. apus, one in which 

 the base of the primary prothallium is sharply delimited, and 

 the other without any clear boundary between the primary and 

 secondary prothallial tissues. 



The Embryo 



The first division in the fertilised ovum is transverse, and 

 as in Lycopodium, the cell next the archegonium neck becomes 



G ^ F 



Fig. 299. — Selagmella Martensii. Development of the embryo (after Pfeffer). A, B, 

 D, E, Successive stages in longitudinal section, X340; C, apical view of a young 

 embryo with four-sided apical cell {x), X340; F, longitudinal section of the primary 

 root, X205; G, apex of the young sporophyte, showing the first dichotomy, X340i 



the suspenso'r. This in Selaginella is much more developed, 

 however, and grows at first more actively than the lower cell 

 from which the embryo proper arises. The upper part of the 



